In the fields of the electronic and electrical industry and the automobile, aircraft and space industries, there is a strong demand in recent years for crystalline thermoplastic resins having high heat resistance of about 300.degree. C. or higher in terms of melting point and moreover easy melt processability.
Recently, poly(arylene thioether-ketones) (hereinafter abbreviated as "PTKs") have drawn attention for their high melting points. Various studies are now under way thereon.
There are some disclosure on PTKs, for example, in Japanese Patent Laid-Open No. 58435/1985, German Offenlegungsschrift No. 34 05 523 A1, Japanese Patent Laid-Open No. 104126/1985, Japanese Patent Laid-Open No. 13347/1972, Indian J. Chem., 21A, 501-502 (May, 1982, Japanese patent Laid-Open No. 221229/1986, U.S. Pat. Nos. 4,716,212, 4,690,972, European Patent Publication No. 0,270,955 A2, European Patent Publication No. 0,274,754 A2, European Patent Publication No. 0,280,325 A2, etc.
Regarding the PTKs described in the above publications, neither molding nor forming has however succeeded to date in accordance with conventional melt processing techniques. Incidentally, the term "conventional melt processing techniques" as used herein means usual melt processing techniques for thermoplastic resins, such as extrusion, injection molding and melt spinning.
The unsuccessful molding or forming of PTKs by conventional melt processing techniques is believed to be attributed to the poor melt stability of the prior art PTKs, which tended to lose their crystallinity or to undergo crosslinking and/or carbonization, resulting in a rapid increase in melt viscosity, upon their melt processing.
The present inventors thus conducted an investigation with a view toward developing a process for economically producing PTKs having melt stability sufficient to permit the application of conventional melt processing techniques. The investigation led to the successful provision of PTKs having significantly improved heat stability upon melting (hereinafter called "melt stability") (Japanese Patent Laid-Open No. 54031/1989).
It has also found that the melt stability of the melt-stable PTKs upon melt processing can be improved further by the addition of a basic compound such as the hydroxide or oxide of a Group IA or Group IIA metal of the periodic table to them (Japanese Patent Application No. 142772/1988).
The melt-stable PTKs obtained as described above have a high melting point, typified by the extremely high melting point of the homopolymer which reaches as high as about 360.degree. C. This is however not all good. Their melt processing temperatures are high accordingly, so that melt processing facilities for high-temperature processing are required. Further, a stringent temperature control is required to perform melt processing without deterioration by heat.
The melt-stable PTKS are generally obtained as fine powders having a particle size of approximately 5-20 .mu.m. This has led to an additional problem upon their production such that they show poor handling properties in their collection step after polymerization, especially in filtration, washing, drying and transportation. Still further problems have also arisen such as poor metering property upon melt processing and occurrence of blocking in hoppers or the like.